1. Field of the Invention
This invention relates to seatbelt systems and more particularly to passive seatbelt systems which automatically fasten or unfasten a restraining seatbelt on a passenger.
2. Prior Art
Seatbelt systems use passenger restraining belts to restrain and protect passengers while they are riding in vehicles. Such systems make it possible to prevent passengers from colliding with dangerous objects during vehicular emergencies such as a collision and improve passenger safety. However, the percentage of passengers who wear seatbelts is extremely low because of difficulty in donning the seatbelt, etc. As a result, passive seatbelt systems have been proposed which make it possible to automatically fasten the seatbelt around the passenger after the passenger has seated himself in the vehicle. Such seatbelt systems include an outer end of the passenger restraining belt arranged so that it can move back and forth in the direction of the length of the vehicle along the vehicle door or a roof side member. The outer end of the seatbelt is moved back and forth in the direction of the length of the vehicle by being connected to a wire driven by a motor which is electrically connected with an electric power source of the vehicle. In this way, the seatbelt can be caused to approach or move away from the passenger seat. Therefore, with such a prior art seatbelt system, the seatbelt can be automatically fastened around the passenger since after the passenger has seated himself in the vehicle, he is held between the passenger seat and seatbelt which is caused to move toward the seat by the passive seatbelt system.
In such conventional passive seatbelt system, however, the driving force of the motor is transmitted to the end of the seatbelt as tension on a wire. Accordingly, it is necessary to mount wire-turning pulleys inside the vehicle body. In particular, large number of wire-turning pulleys are required in order to optimize the arrangement of various parts of the mechanism and to obtain suitable seatbelt movement. Furthermore, it is necessary to regulate and control the wire tension in an appropriate manner. In addition, it is necessary to resolve a contradictory problem. From the standpoint of motor output and noise generated during the operation of the seatbelt system, it is desirable that the tension on the wire be weak. From the standpoint of reliable transmission of driving force, however, it is desirable that such tension be strong.